Today, portable terminals such as mobile phones (particularly, smartphones), MP3 players, digital cameras, tablet PCs and the like are an inextricable part of real life. In particular, the proportion of smartphones and tablet PCs actively used worldwide is remarkably increasing and thus the demand for a power charging device for regularly supplying power to the portable terminal is rapidly increasing.
Users generally charge their portable terminals at their bedtime. However, since recent portable terminals are widely used for users' life style and are equipped with various functions (in particular, accessing the Internet) that have never existed before, power consumption of the battery greatly increases compared to the past. Therefore, the battery of the portable terminal may discharge anytime even in an emergency case and this situation may embarrass users who desperately need portable terminals in real life. Therefore, there is an increasing demand for a device which can regularly supply power to the portable terminal.
One of the alternatives for supplying power to the portable terminal is a piezoelectric generator. The piezoelectric generator is a power generator using a piezoelectric material which causes a piezoelectric phenomenon in which polarization (electric energy) is induced in material when mechanical energy (wind, vibration, or the like) is externally applied.
Most of the modern piezoelectric generators are generally designed to generate power by transmitting vibration energy to one end of a piezoelectric material using a configuration of cantilever or bimorph (or unimorph) and having the shape of the piezoelectric material changed (crooked or bent). The most effective and essential factor in the method for transmitting vibration energy to a piezoelectric is combining a mass of appropriate weight with one end of the piezoelectric material.
However, applying such a piezoelectric generator to portable terminals goes against the current consumer trends for the portable terminals. This is because the mass included in the piezoelectric generator increases weight and volume of the portable terminal.
The current consumer trends for the portable terminals focus on smaller, lighter, and slimmer devices. Therefore, research on a piezoelectric generator which can regularly supply power to a portable terminal without increasing weight and volume of the portable terminal is being conducted.